Color filters are used as optical filters for various electronic products, such as liquid crystal displays (LCDs), cameras, and the like. Color filters are thin film-type optical parts extracting more than 3 colors from a white light and forming fine pixel units. The pixel has a size of tens to hundreds of micrometers. Color filters can have a laminate structure including a black matrix layer with a predetermined pattern to block a boundary between pixels and a pixel region including a plurality of colors (in general, three primary colors of red (G), green (G), and blue (B)) sequentially arranged in a predetermined order on a transparent substrate. In general, methods for fabricating the colored thin film of a color filter include dyeing, printing, electrophoretic deposition (EPD), and pigment dispersion, among others. Currently, such methods are used to manufacture LCDs for mobile phones, laptops, monitors, TVs, and the like.
The dyeing method forms a colored film by forming an image on a glass substrate with a dyeing agent and then dyeing the image with a direct dye. Examples of the dyeing agent used in fabricating colored thin films include a natural photosensitive resin such as gelatin and the like, an amine-modified polyvinyl alcohol, an amine-modified acrylic-based resin, and the like. However, the dyeing process may be complex and long, since it should include resist-printing whenever a color needs to be changed to form a multicolored thin film on the same substrate. In addition, many generally-used dyes and resins may have good color vividness and dispersion but also poor color fastness, water resistance, and heat resistance, which are very important characteristics.
The printing method forms a colored thin film by printing an ink prepared by dispersing a pigment into a thermally curable or photocurable resin and curing the resin with the pigment dispersed therein with heat or light. This method may decrease material costs compared with other methods. It can be difficult, however, to form a fine and precise image and acquire a uniform thin film layer using printing methods.
Korean Patent Laid-Open Publication No. 1996-0011513 discloses formation of a color filter in an inkjet method. However, the resultant color filter suffers problems similar to that of a color filter made by dyeing, for example, deteriorated durability and heat resistance, because this method also uses a dye-type color resist composition dispersed from a nozzle to accomplish fine and precise color printing. Korean Patent Laid-Open Publication No. 1996-0029904 discloses formation of a color filter in an electrophoretic deposition (EPD) method including an electrical precipitation method. The electrophoretic deposition (EPD) method may provide a precisely-colored thin film with excellent heat resistance and color fastness, since it uses a pigment. However, this method may not be useful for fabricating a highly precise color filter requiring a finer electrode pattern for a more precise pixel in the future, because the colored thin film may be stained or thicker at both ends due to electrical resistance.
In contrast, the pigment dispersion method forms a colored film by repeating a series of processes such as coating, patternwise-exposing to light, removing non-exposed part by using a solvent, and heat-curing a photopolymer composition including a coloring agent on a transparent substrate including a black matrix. This method can improve heat resistance and durability, which are very important characteristics for a color filter, and thus, can provide a uniformly-thick film.
However, the pigment dispersion method cannot provide color characteristics, such as luminance, contrast ratio, and the like, currently required in various products. Accordingly, there is a need for a method for making a color filter that can minimize or eliminate deteriorated contrast ratio and additionally provide high luminance.